More robust size factor parsing.

There was a bug occurring when a library name was contained in another.

bam2bigwig.sh

@@ -82,7 +82,7 @@ then
     if [ -f ${norm} ]
     then
         echo "reading scaling factor for ${lib_name} in ${norm}"
-        size=$(grep "${lib_name}" ${norm} | cut -f2)
+        size=$(grep -w "^${lib_name}" ${norm} | cut -f2)
         if [ ! ${size} ]
         then
             error_exit "size could not be found on column 2, line ${lib_name} of ${norm}"